This invention relates to a differential lever actuator which is useful, among others, in actuating a printing rod of a printing element in a printing head of an impact printer.
A differential lever actuator is described in U.S. patent application Ser. No. 381,479 filed May 24, 1982, now U.S. Pat. No. 4,435,666, by Izumu Fukui et al, assignors to the present assignee. A differential lever actuator comprises a driving member having an axis and a first and a second end transversely of the axis. The driving member is preferably an electroexpansive body of a rectangular prismal shape. At any rate, the first end is fixed to a base or holding member. The second end is susceptible to a linear displacement along the axis. First and second lever members are attached to the base member at first and second fulcrum points, respectively, and to the second end at first and second power points, respectively. The fulcrum and the power points are so called merely because each lever member serves as a lever, as will presently become clear. The lever is for getting a greater displacement from the linear displacement.
First and second plate-shaped resilient transmission members have principal surfaces perpendicular to a reference plane including the axis and the first and the second power points, and are attached to the first and the second lever members at first and second weight points, respectively. A third lever member, which is herein named a differential lever member because of the reason which will shortly become clear, is carried by the first and the second transmission members at first and second predetermined points of the differential lever member, respectively. The first and second lever members give amplified displacements to the respective weight points in opposite senses. The transmission members therefore differentially transmit forces to the differential lever member to give a further, amplified displacement to that end of the differential lever member which is more remote from one of the predetermined points than the other.
In a conventional differential lever actuator, at least one of the transmission members often breaks or is liable to damage, particularly when the differential lever actuator is repeatedly operated many times. It has now been found and confirmed that the breakage results from a complicated deformation to which the transmission member is subjected during operation. Furthermore, the complicated deformation reduces the displacement transmitted to the differential lever member through the transmission member and results in wasteful consumption of energy which would otherwise be effective in actuating the differential lever member. In other words, the complicated deformation not only caused damage to the transmission members, but also adversely affects the efficiency of operation of the differential lever actuator.